ASP.NET PDF Viewer using C#, VB/NET

This will have the potentially surprising result that the query could return different files every time it runs, even if the underlying data has not changed. Remember, the expression in the where clause gets converted into an anonymous method, which will be invoked once for every item in the query s source. The first time this runs, the local x variable will be incremented once for every file on the disk. If the query is executed again, that ll happen again nothing will reset x to its original state. Moreover, queries are often executed sometime after the point at which they are created, which can make code with side effects very hard to follow looking at the code in Example 8-8 it s not possible to say exactly when x will be modified. We d need more context to know that when exactly is the bigFiles query evaluated How many times In practice, it is important to avoid side effects in queries. This extends beyond simple things such as the ++ operator you also need to be careful about invoking methods from within a query expression. You ll want to avoid methods that change the state of your application. It s usually OK for expressions in a query to read variables from the surrounding scope, though. A small modification to Example 8-8 illustrates one way you could exploit this (see Example 8-9).

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int minSize = 10000; var bigFiles = from file in GetAllFilesInDirectory(@"c:\") where new FileInfo(file).Length > minSize select file; var filesOver10k = bigFiles.ToArray(); minSize = 100000; var filesOver100k = bigFiles.ToArray(); minSize = 1000000;

Drupal has a low-volume e-mail list dedicated to announcing security issues affecting Drupal core and contributed modules. It s also good to sign up for the Drupal newsletter if you want to hear about Drupalrelated conferences and other happenings (see Figure 11-3). Signing up is relatively easy: 1. 2. 3. 4. Create an account at http://drupal.org; if you already have one, sign in. Navigate to the Your Dashboard page or alternately to http://drupal.org/user. Click the Edit link, and then click the My newsletters tab. Select the security announcements check box, and click save.

var filesOver1MB = bigFiles.ToArray(); minSize = 10000000; var filesOver10MB = bigFiles.ToArray();

object database 124 object-oriented principles 281 object-oriented software 22 object-to-object mapper 258 ObjectDataSource 99 ObjectFactory.GetInstance 196 ObjectFactory.Initialize() 194 objects, data-transfer 120 OnActionExecuted 377 OnActionExecuting 377 378 OnAuthorization 154, 377 OnBegin 187 188 onclick event 170 OnComplete 187 OnException 377 OnExecutingMethod 379 OnFailure 187 onion architecture 324 OnResultExecuted 377 OnResultExecuting 377 OnSuccess 187 Oracle 329 sequence functionality 331 organization 311 Osherove, Roy 61, 64 out-of-process call 333 output caching 103 OutputCache 103 104 OutputRouteDiagnostics 352

This query makes use of a local variable as before, but this query simply reads the value rather than modifying it. By changing the value of that variable, we can modify how the query behaves the next time it is evaluated. (The call to ToArray() executes the query and puts the results into an array. This is one way of forcing an immediate execution of the query.)

LINQ operators all share a common characteristic: they do not modify the data they work on. For example, you can get LINQ to sort the results of a query, but unlike Array.Sort or List<T>.Sort, which both modify the order of an existing collection, sorting in LINQ works by producing a new IEnumerable<T> which returns objects in the specified order. The original collection is not modified. This is similar in style to .NET s string type. The string class provides various methods that look like they will modify the string, such as Trim, ToUpper, and Replace. But strings are immutable, so all of these methods work by building a new string you get a modified copy, leaving the original intact. LINQ never tries to modify sources, so it s able to work with immutable sources. LINQ to Objects relies on IEnumerable<T>, which does not provide any mechanism for modifying the contents or order of the underlying collection.

NameFormatter 261, 263 264, 266 namespaces 312 naming conventions 260, 262 NAnt 80, 252 257 XCOPY deployment 79 NAntContrib 253 NBehave 59, 288 .NET 3.5 SP1 248 .NET 4 83, 96, 99 New Project 5 NewtonSoft 182

Of course, LINQ does not require sources to be immutable. IEnumera ble<T> can be implemented by modifiable and immutable classes alike. The point is that LINQ will never attempt to modify its source collections.

This approach is sometimes described as a functional style. Functional programming languages such as F# tend to have this characteristic just as mathematical functions such as addition, multiplication, and trigonometric functions do not modify their inputs, neither does purely functional code. Instead, it generates new information based on its inputs new enumerations layered on top of input enumerations in the case of LINQ. C# is not a purely functional language it s possible and indeed common to write code that modifies things but that doesn t stop you from using a functional style, as LINQ shows. Functional code is often highly composable it tends to lead to APIs whose features can easily be combined in all sorts of different ways. This in turn can lead to more maintainable code small, simple features are easier to design, develop, and test than